1. Field of the Invention
This invention is concerned with water-based coating compositions containing polyvinyl chloride.
2. Description of the Prior Art
Vinyl resins have been used extensively in the packaging industry because of their desirable properties of hardness, flexibility, product resistance, water resistance, and freedom from taste. Such resins are applied as solutions in organic solvents, which have to be removed, e.g., by evaporation into the air. Because, however, of air pollution regulations and standards, it has become desirable to use water as at least the major portion of the volatile vehicle.
Most vinyl polymers, particularly polyvinyl chloride, do not have functional groups on the polymer that can react with a solubilizing agent such as ammonia or an amine to convert the resin into a water-soluble material. It has been proposed to apply PVC as a hydrosol, i.e., PVC dispersed in water by use of wetting agents (surfactants). Films from such hydrosols have poor water resistance, probably because the wetting agent remains in the dried film and causes poor performance.
In U.S. Pat. No. 3,305,505, it is taught to fortify a resin latex with an amine or ammonium salt of a copolymer of the resin and meleic anhydride. The patentee specifically teaches that interpolymers of maleic anhydride with monomers differing from those of the latex will not fortify the latex.
It is the discovery of this invention that PVC can be dispersed in solution of a water-dilutable resin other than vinyl chloride-maleic anhydride solubilized with ammonia, NH.sub.4 OH or an amine, the solvent being water or a mixture of water and an alcohol or ether alcohol. When applied to a substrate and dried there is obtained a film suitable for packaging applications.